How does an external tower style bathtub drain work?

Question

I have this style tub drain and can't figure out how it works. Does it simply block the flow of water when lowered? Or is there something more complicated happening?

My tub has stopped draining and when I removed the cylinder from the drain tower it came right out, but this did not affect the stoppage. I wonder if it should be attached to something, but can not see into the tube well enough.

I should add that I had been trying to unblock the drain and used a plunger on it. So there is a possibility that I plunged the clog(s) into a more blocking state, but I suspect that the pressure of the plunger interfered with something mechanical, because the water isn't receding at all, even after some hours.

Answer 1

It's called a "standing waste". It works just like you say. The cone at the base of the inner tube seals against a flange and the water must fill the outer tube (attached to your floor) before (over)flowing down the inner tube. Here's a pic since words are useless for describing this kind of thing.

Here's some in-depth discussion on resolving a clog on one of these.

if you see water in the tube at the same height as in the tub, you should snake down the tube. If not, the blockage is between the drain and the standing waste and you should snake down the tub drain.

I suspect the blockage is downstream of the standing waste since the plunger was ineffective. Try sealing the top of the standing waste tube while plunging before resorting to the snake.